Update variables.md explanation of parameters

[artkuo]

I was confused by this example at multiple levels. I didn't understand what "Parameters set" means, is there a whole set of parameters somewhere? I didn't understand Parameter(i) because i looks like an index, not a value. I didn't get how there can be x in SecondOrderCone and x in Parameter(i), same syntax but seemingly different concepts. The values are eventually revealed later on in example, but even then I was confused.

This change is to try to be more explicit about what's going on, in case others are as obtuse as I am. I hope something like this will be clearer.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.58%. Comparing base (99cdc4c) to head (6a8df0d).

Additional details and impacted files

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##           master    #3916   +/-   ##
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  Coverage   99.58%   99.58%           
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  Files          43       43           
  Lines        6059     6059           
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  Hits         6034     6034           
  Misses         25       25           

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[artkuo]

The build failed because it failed a test on builders_decomposition.jl. I don't think it's related to this pull request, which is just changing some non-executing text in a markdown file.

[odow]

Hi @artkuo, thanks for opening the PR!

Don't worry about the failure. It is my fault: #3917

To answer some of your questions:

is there a whole set of parameters somewhere

JuMP uses "set" to mean the domains that constraint functions belong to.

If you have time, you might want to read https://arxiv.org/abs/2002.03447. Or you can take a look at https://jump.dev/JuMP.jl/stable/moi/manual/standard_form/

So SecondOrderCone() is the set https://jump.dev/JuMP.jl/stable/api/JuMP/#SecondOrderCone.

Parameter(value) is the singleton mathematical set {value}. See

https://jump.dev/JuMP.jl/stable/api/JuMP/#Parameter

which is really just a synonym for:

https://jump.dev/JuMP.jl/stable/moi/reference/standard_form/#MathOptInterface.Parameter

because i looks like an index, not a value

It's a value 😄

[odow]

I made a change. Is that better?

[artkuo]

Yes, that looks great! Sorry about my questions, they were meant to be rhetorical but were eventually resolved. I should have put that under "This change is..." I think your revision is very nice, thanks. The 2.0*i removes potential confusion between index and value.

[artkuo]

I'm was confused, I clicked "close with comment" thinking your revision would be merged. But it looks like that just killed the pull request. I'm leaving open in case you need to see that your revision still needs to be merged. Please close this if and when appropriate.

[odow]

I'm was confused, I clicked "close with comment" thinking your revision would be merged.

I have the power to edit your PR directly 😄 When I merge it, it'll attribute you as the author.